Investments (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Investments [Abstract]
Net unrealized gains on impaired securities	$ 25.6		$ 25.1
Other-than-temporary impairments	1.6
Net other-than-temporary impairment losses on securities recognized in earnings	1.9	1.4
Amount transferred from unrealized losses in accumulated other comprehensive income	0.3	0.2
OTTI of fixed maturities and equity securities		1.2
Restricted assets, fixed maturities	410.0
Restricted assets, cash and cash equivalents	69.0
Overseas deposits	$ 148.1		$ 135.1

Total debt and equity financial instruments including: (1) securities held-to-maturity, (2) trading securities, and (3) securities available-for-sale that are pledged to one or more secured parties who have the right to buy, sell, or re-pledge the collateral.

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The carrying amounts of cash and cash equivalent items which are restricted as to withdrawal or usage. Restrictions may include legally restricted deposits held as compensating balances against borrowing arrangements, contracts entered into with others, or entity statements of intention with regard to particular deposits; however, time deposits and short-term certificates of deposit are not generally included in legally restricted deposits. Excludes compensating balance arrangements that are not agreements which legally restrict the use of cash amounts shown on the balance sheet. This element is for unclassified presentations; for classified presentations there is a separate and distinct element.

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